governor romney, he's a good debater. i'm just reporter: the presiden . aying in nevada to prepare weekend and is heading to mpairadotoday. ca watchs say all thre chalrtunity forepuicr the n er to hava me- changing moment. new jers governor chris christieto cbs's bob schieffer romney is pable of that. >> the whole race will be turned upside down come thursday morning. >> reporter: but romney's running mate paul ryan downplayed the debate. >> i don't think one event will make or break the campaign. >> reporter: romney is trailing in the polls in most must-win states. tara mergener for cbs news, the white house. >>> in california, 10% of parents exempt their children from the mandatory school vaccinations. yesterday, governor brown signed a new law making vaccine waivers tougher to get. but a last-minute change is giving parents a new out. >> reporter: at tri-valley pediatrics, this 10-month-old is getting a flu shot. his mother talked to the doctor before making her decision. >> we definitely rely on our pediatrician as an expert. we put our son's health i